Currently, a number of technologies have been proposed to increase the storage areal density of storage devices such as hard disk drives. One example of such technologies is heat-assisted magnetic recording (HAMR). In traditional storage devices, the minimum size of a magnetic field limits the amount of data stored in a given magnetic storage device. Thus, the regions of the hard disk storage used to store data may only be decreased while the magnetic fields are capable of supporting data writes. HAMR attempts to remedy this physical limitation by briefly heating the disk surface during writing which results in smaller magnetic fields achievable and, thus, smaller bit surfaces.
Another technique to increase storage areal density is bit-patterned media (BPM). Using BPM, data is stored in isolated magnetic islands as compared to existing techniques of storing bits of data using multiple magnetic grains. These magnetic islands are patterned using a precursor magnetic film (e.g., using nanolithography).
Both of these techniques over experimental improvements in storage areal density, however, they suffer from significant technical deficiencies. First, the underlying technologies in HAMR and BPM are currently experimental. Second, the existing techniques require fundamental changes to storage devices themselves. For example, HAMR requires a heating element to heat the magnetic surface temporarily. Thus, no existing storage devices can benefit from HAMR. BPM similarly requires modifications to the magnetic surface via nanolithography. Thus, current devices must be completely replaced. Third, the technical processes for implementing HAMR and BPM are complex, time-consuming, and expensive. The use of complex heating elements and nanolithography inherently increase the costs of manufacturing a given storage device. Fourth, as more data is stored using the above techniques, the quality of data is adversely affected due to noise resulting from the compacted data.
Another technique for increasing storage areal density in magnetic storage devices is shingled magnetic recording (SMR). In a conventional magnetic storage device, depicted in FIG. 7A, a given track is written to by a writer (also referred to as a “write head”) that extends the entire height of the track. A reader (also referred to as a “read head”) is thinner than the height of the track and reads from a portion of the track smaller than the height of the track. A guard space is situated between each track to avoid interference of the track magnetic fields.
In contrast, in SMR (illustrated in FIG. 7B) the tracks and the read portions overlap, forming a shingled pattern. The read head is appropriately reduced to handle the trimmed tracks. SMR, however, suffers from specific technical problems. First, SMR drive still cannot flexibly append extra bits with fixed sector size conventions. Applications needing to store extra bytes into each sector, however, and while SMR drives increase the areal density by removing the guard space among tracks and overlapping the tracks in the radial direction of the platters, the number of bits can be stored in one track keeps same as before. Second, SMR devices change conventional HDD operations. The concept of a trimmed track, or band, is introduced, and any modification in the band that is 128 or 256 MB requires the whole band to be read out and rewritten together. As a result, the random write performance of SMR is lower than that of a conventional drive. Third, SMR management is based on the unit of a trimmed track or band. When each sector varies its size individually, it causes many varieties for the band. This variation is complex to handle using existing SMR techniques.
Thus, there currently exists a need in the art to increase the storage areal density of a storage device without incurring the technical deficiencies in more experimental technologies. In one embodiment, the disclosed embodiments additionally may be applied to SMR drives as well as conventional drives.